an overview of distributed generation in power sector - IJSTM

International Journal of Science, Technology & Management Volume No 04, Special Issue No. 01, March 2015

www.ijstm.com ISSN (online): 2394-1537

AN OVERVIEW OF DISTRIBUTED GENERATION IN POWER SECTOR M. Kumar1, C. Samuel2, A. Jaiswal3 1,2,3,

Department of Mechanical Engineering, Indian Institute of Technology (BHU), Varanasi, (India)

ABSTRACT In present era, dependence of human life over technology has increased. Today we can’t imagine human life without technology, because of the technological necessity in day to day life. Increase in demand of technology has also increased demand of electricity. Earlier, generation of electricity was mostly based upon central power generating unit and transmission was also over long transmission line to meet far away load demand. Transfer of power through long transmission line or network was resulting in transmission losses and reliability problems. For overcoming these issues a new technology has emerged called Distributed Generation. In this method the electricity is generated near to load demand with small generating units. Utilization of new energy sources in DG, for example utilization of environmental friendly renewable energy sources also helps to reduce transmission losses. The paper defines Distributed Generation and compares it with conventional power generation approach. It elaborates the concept behind the development of Distributed Generation; technologies used; its advantages and limitations. It also focuses on why it should be prefer and how it helps to minimize energy losses. This work analyzes Distributed Generation over central power generation and discusses the impact of technology in the coming future.

Keywords: Distributed Generation (DG), Transmission & Distribution, Transmission Network, Renewable Energy Sources I. INTRODUCTION Generation of electricity mostly depends upon centralised power generating facilities, for example coal, oil and gas powered, nuclear, large solar plants or hydro power plants. Centralised power generating units are located at distant places from load demand. Transmission of power from generating units to load demand causes transmission loss, quality of power and reliability problems. Facilities utilised by centralised power generating units for example coal, oil & gas adversely affect the environment. To overcome these issues power sectors are adopting a new technology called Distributed generation. Electric power research institute defines DG system as a small-scale based modular energy conversion unit located near to load demand ranged between 1kw to 50MW [1]. In this technology generation units are located near to load demand with small scale generating capacities and directly connected to the distribution network to meet uncontrollable demand with more flexibility. It is interconnected to the same transmission grid as of central stations for the reason of reliability. Reliable power sources minimize interruption of power supply or power outages. DG also helps to enhance quality of power i.e. voltage levels, fluctuations and disturbances. There are several technical and economical issues in the integration of these resources into a grid. It greatly reduces transmission loss and is a reliable power source. Technical problems arise in the areas of power quality,

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voltage stability, reliability, protection and control [2]. Behaviour of protective devices on the grid must be examined for all combinations of distribution and central station generation [3]. A large deployment of DG may affect grid-wide functions such as frequency control and allocation of reserves [4]. For this, there will be a need of good coordination control and better as well as bigger interconnections among them. DGs are expensive per watt electricity generation to central generators due to its high initial setup cost. But As per sources, the current initial costs of DG systems are decreasing gradually, as many countries are increasing their capacity [5]. In the last decade many countries have started the process of liberalization of their electrical systems, opening access to Transmission & Distribution grids. India is also liberalising its power sector and reforming electricity sector by increasing competition with flexibility of participation of private sector. Still With the liberalisation and participation of private sectors, India uses far less electricity per capita than developed countries, i.e. only about 900KWh per capita in India compared with 7,000KWh per capita in Europe and 14,000kwh in the US. As per sources, the electricity generation capacity will grow in India from about 225GW in 2013 to 700GW by 2032 to meet rising demand [6]. Today the DG is mostly based upon diesel engines that are used for back-up power (in the event of grid failure) and operate at very low load factors. Also the share of the energy generation from DG is marginal (about 2–3% of the total generation). Other than the diesel engines, the DG options that are being promoted in India are modern renewable energy based system [7]. Penetration of renewable energy sources play major role to enhance DG systems because of its small scale capacity and environment friendly nature. In this research work, we have gone through various author‘s contribution over penetration of DG in electricity sector. We have discussed advantages of this new technology and compared with central power generation system. In our work we have emphasized on acceptance of this new technology along with its advantages and limitations. Organization of the paper is as follows; section 2 explains Distributed Generation and comparison with central power generation. Use of DG, different types of DG Technologies and its applications are reviewed in sections 3 and 4. Benefits of DG and its Challenges of DG are discussed in section 5 and 6. The section 7 summarizes with Conclusions.

II.DISTRIBUTED GENERATION AND COMPARISON WITH CENTRAL POWER GENERATION Different terms and definitions are used related to DG in different literature. For example, Anglo-American countries often use the term ‗embedded generation‘, North-American countries use the term ‗dispersed generation‘, and Europe and parts of Asia, uses the term ‗decentralised generation‘. Analysis of the relevant literature has shown the relevant definitions of DG which are derived in terms of capacities: 1. The electric power research Institute defined DG as generation from a few kilowatts up to 50MW [1], 2. According to the Gas Research Institute, DG is in between 25KW and 25MW [8], 3. Preston and Rastler defined as ‗ranging the size from a few kilowatts to over 100 MW‘ [9], 4. Cardell defined DG as generation between 500KW and 1MW [10], 5. The international conference on Large High Voltage Electric Systems (CIGRE) defined DG as ‗smaller than 50-100MW‘ [11],

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―DG can be defined as effective and efficient fulfilment of load demand with small generating units ranging between 50KW to 50MW near to load demand‖. As per government regulations of different countries, the rating of each distributed power station varies. For example; In English and Welsh market, DG with a capacity of less than 100MW are not centrally dispatched and if the capacity is less than 50MW, the power output can‘t be traded via the wholesale market [12]. Therefore, in English and Welsh market DG predominantly used for power units with less than 100MW capacity. As per Swedish legislation DG is used for generation of electricity up to 1500KW [14]. On the other hand some of the proposed offshore wind farms for Sweden have a maximum capacity of up to 1000MWand this would still be considered DG as they plan to use 1500KW wind turbines [13]. Here we will see comparison of DG with central power generation. Comparison of Distributed Generation with central power generation on the basis of power flow from generating unit to load demand is given below:

Central Power Generation

vs

Distributed Generation

Fig.-1 Comparisons of DG with central generation approach Multiple problems associated with central power generation, for example, are power losses through transmission, power theft, reliability and quality of power. Long distance power transmission also creates theft of power which is a big issue. Developing countries like India are mainly facing problems like lack of conventional energy resources, old technology, and power losses through transmission. In 2010, average electricity losses in India during Transmission & Distribution were about 24% of total loss, while losses because of consumer theft or billing deficiencies added another 10–15% [14]. If current average transmission & distribution losses remain same (32%), India will need to add about 135 GW of power generation capacity, before 2017, to satisfy the expected demand [15]. Local production has no electric transportation losses compared to long distance power lines or energy losses from the Joule effect in transformers where in general 815% of the energy gets lost [16].The developed countries like America and Europe have advantage of advanced technology which is the reason of their minimum transmission power losses and theft of power. On other side, due to lack of coal reservoir, thermal power generating units suffers for consistent coal shortage conditions and works on high risk of unit shutdown. DG resources can play a big role to meet the huge and rising electricity demand and supply gap. Thermal power generating units pollutes the environment and

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increases global warming. China, world‘s major polluter, plans to reduce its CO2 emissions by 40% to 45% per unit GDP by 2020 from a 2005 baseline by implementing a carbon trading market that will penalise major polluters [17]. Ongoing 20 years of discussions and consultation about sustainable development, the world‘s climate and its biodiversity are still deteriorating [18]. With the help of DG system and renewable energy sources we can overcome all such issues. DG uses generating units sized between 1KW to 50MW near to load demand as compared to central power generating units sized between 100MW to 1GW at distant from load demand. Applications of different types of technology in DG have changed the way of operating electric power systems and utilization of renewable energy sources makes DG clean and environment friendly power generating system.

III. USE OF DG In the past years, there have been good development of small scale generation technologies, but still they failed to push the ―economy of scale‖ out of the system, because of its high initial setup cost. But other than this, other benefits make it desirable and thus its utilisation is increasing with each days passing. Also global warming and shortage of conventional energy resources make it necessary to look after clean and renewable energy sources. As compared to traditional diesel generator set, renewable energy is used for DG to reduce global warming. Now we will see use of DG due to market liberalisation and environmental concern [20]:

3.1 Market liberalisation Now electricity suppliers are more concern with their interest in DG, because they see it as a tool that can help them to fill in niches in a liberalised market. In which, customers will look for the electricity service that will suit best for them. Weights assign to features of electricity supply and DG technologies from the different customers; can help electricity suppliers to supply the type of electricity service that they want. In changing market conditions, DG allows electricity suppliers in the electricity sector to respond in a flexible way. As compared to larger central power plants in many cases, DG provides this flexibility because of its small sizes and the short construction lead times. According to the IEA [19], the flexibility of this new technology can be understood when economic assessments of DG are made. We can get further knowledge from different areas which are discussed below: 3.1.1 Peak Load Shaving Many DG technologies are indeed flexible in several respects: operation, size and expandability. Making use of DG gives flexibility of electricity price evolutions. DG then serves as a hedge against these price fluctuations. Europe increased their DG efficiency for heat applications with the help of renewable energy sources [20]. In 2013 India faced some black out conditions, which indicates lack of flexibility and reliability in electricity supply. For reliable and flexible power sources demand of DG in India has increased. 3.1.2 Power Quality WE can have smaller voltage deviations, apart from large voltage drops to near zero. Voltage deviation shows level of power quality. Degree of power quality refers to the power characteristics align with the ideal sinusoidal voltage and current waveform, with current and voltage in balance [21]. Inadequate power quality may caused by (1) interruptions, voltage dips, and transients which occur due to switching operations and failures in the network, and (2) phase imbalance , flicker (fast voltage variations), and harmonics. The nature of these

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disturbances is related to the ‗short-circuit capacity‘. It is important for network operators to guarantee a specified minimum short-circuit capacity, to protect the system from degradation in power quality [22]. Ambiguity occurs when we go for find a relation between DG and power quality. There are many authors who stress over the healing effects of DG for power quality problems. DG can contribute voltage support in areas where it is difficult, as connecting DG generally leads to rise in voltage in the network [19]. Dondi et al. [20] also mentioned the potential positive effects of DG for voltage support and power factor corrections. 3.1.3 Reliability Unreliable power source gives problem related to repetitive power interruptions, which are voltage drops to near zero in electricity supply. Due to liberalisation of energy markets, customers are more aware of the value of reliable electricity supply. In many European countries, the reliability level is very high, mainly because of high engineering standards. In general, compared to voltage fluctuation, customers do not really care about supply interruptions because they do not feel it as a risk. Voltage instability can damage costly electrical and electronic equipment. Dependence of human life over technology demands continuous power supply. Now a day, customer demand has increased for reliable power sources. Continuous demand implies high investment and maintenance costs for the generation and network infrastructure. In industries like chemicals, petroleum, refining, paper, metal, and telecommunications having a reliable power supply is very important. Investors of these firms facing poor reliability level of power supply to invest in these industries. DG technology helps to increase reliability level of power supply to fulfil customer demand up to the desired level [20]. 3.1.4. Alternative to expansion DG could serve as a substitute for investments in Transmission & Distribution capacity (demand for DG from T&D companies). But, this is possible only to the extent that alternative primary fuels are also locally available in sufficient quantities so that it can give a better alternative power generation option. According to the IEA [19], on-site production of electricity could result in 30% of cost savings during Transmission & Distribution. It directly impacts the increase demand of DG from the customer. Generally it is seen, if density of customer is less, the share of Transmission & Distribution costs in the overall price becomes large (above 40% for households) [19]. As per System operator‘s point of view, DG units can be a substitute for investments in Transmission & Distribution capacity. DG unit can be used as an alternative to connecting a customer to the grid in a ‗stand alone‘ application. Well chosen DG locations like close to the load can also contribute to reduced grid losses. The IEA [19] reports average grid losses of 6.8% in the OECD countries. According to Dondi et al. [20], cost savings of 10–15% can be achieved using DG technology in this way.

3.2. Environmental Concerns In present scenario, environmental policies or concerns are probably the major driving forces for the demand of DG, because of increased utilization of renewable energy sources. Environmental regulation force players in the electricity market are looking for cleaner energy- and cost-efficient solutions. By the use of DG we can optimise the energy consumption of firms that have a large demand for both heat and electricity [20]. Also, most government policies which have aimed to promote the use of renewable will also result in an increased impact of DG technologies, as renewable, except for large hydro, have a decentralised nature. More explanations related to environmental concern are given below: 3.2.1. Combined Generation of Heat and Electricity

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It makes sense to consider the combined generation of heat and electricity on sites where there is a considerable and relatively constant demand for heat, instead of generating the heat in a separate boiler and buying electricity from the grid. This technology is called cogeneration technology and cogeneration units create a large segment of the DG market. Compared to separate fossil-fired generation of heat and electricity, CHP generation may result in a primary energy conservation, varying from 10% to 30%, depending on the size (and efficiency) of the cogeneration units [20, 23, and 24]. The avoided emissions are in a first approximation similar to the amount of energy saving, although the interaction with the global electricity generation system also plays a role. 3.2.2. Efficient Use of Cheap Fuel Opportunities Installation of DG gives opportunity to use cheap fuel sources. For example, in the proximity of landfills, DG units used to burn landfill gases to generate electricity. But at local level biomass resources may also be envisaged. Currently the liberalisation of the electricity market and increased environmental concerns in developing countries both induce an increased interest in DG applications and thus also in innovations in the appropriate technologies. However, the technical, economic and environmental challenges will be to optimally integrate this increasing number of small generation units in an electricity system that up to now has been very centralised, integrated and planned [20]. 3.2.3 Use of Renewable Energy Sources Due to environmental benefits, developed and developing countries are moving towards use of renewable energy sources to generate electricity. It reduces green house gases and controls acidification. Small scale generation capacities of renewable energy sources are making this favourable for DG. Solar and wind energy are playing major role in DG, because of its availability. Various developed and developing countries are increasing use of renewable energy for generation of electricity [25].

IV. DIFFERENT TYPES OF DG TECHNOLOGIES AND ITS APPLICATIONS DG shows a range of technologies for example fuel cells, reciprocating engines, small gas combustion turbines, micro-turbines, load reduction and other energy management technologies. In the table given below, we are discussing about different types of DG technologies and their fuel choices along with their benefits and drawbacks: DG Technologies

Fuel Choices

Benefits

Drawbacks

Micro turbines

Natural gas, propane,

• Thermal recovery

• Insufficient thermal

Micro turbines are small combustion

diesel, multi-fuel

improves efficiency

output for industrial

turbines that produce power ranged

• Thermal output for

applications

between 25 kW and 500 kW. Micro

residential or small

turbines were derived from

commercial applications

turbocharger technologies found in

• Operable as base, peaking,

large trucks or the turbines in aircraft

or back-up

auxiliary power units (APUs).

• Commercially available in

Efficiency of this technology is 28%

limited quantities

to 33% Small Gas Combustion Turbines

Natural gas, distillate,

• Highly efficient when

• Potentially onerous

For DG small gas combustion turbine

methane, dual fuel

used with thermal recovery

siting and permitting

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generators typically range in size

• Technology commercially

requirements

from about 500 kW up to 25 MW.

available today—most

• Environmental issues—


likely candidate for on-site

emissions and noise

to 40%

needs >3 MW in DG

• Possible on-site fuel

application

storage needs

• Can operate base load, back-up, or peaking load • Several manufacturers • Relatively low installed costs Internal Combustion Engines

Diesel, natural gas,

• Bulk power delivered

• Capital is only being

Internal combustion engines converts

propane, bio-gas,

when utility is unavailable

used when back-up

the energy contained in a fuel into

other petroleum

• Fast start-up allows less

generator is running

mechanical power. This mechanical

distillates

sensitive processes to be

• Marginal cost of

power is used to rotate a shaft in the

served without need for

production favours utility

engine. A generator is attached to the

UPSs (for use of emergency

source in rare occasions

IC engine to convert the rotational

lighting, HVAC, elevators,

• Environmental issues

motion into power. They are

some manufacturing

like carbon emissions and

available from small sizes 5 kW to

processes)

noise

large generators e.g., 7 MW.

• Very mature, stable

• Possible on-site fuel


technology

storage needs

to 37%

• Can be paralleled to grid or other generators with controls package • Can be very efficient when combined with heat recovery

Stirling Engines

Air, Hydrogen,

-Stirling engines can run

- Stirling engine designs

A Stirling engine is a heat engine that

Helium

directly on any available

require heat

operates by cyclic compression and

heat source

exchangers for heat input

expansion of air or other gas at

- They require less

and for heat output, and

different temperatures. The Stirling

lubricant and last longer

material requirements for

engine is noted for high efficiency

than equivalents on other

this substantially increase

compared to steam engines, quiet

reciprocating engine types

the cost of the engine

operation, and its ability to use

- No valves are needed, and

- Dissipation of waste

almost any heat sources. Stirling

the burner system can be

heat is especially

engines are cost competitive up to

relatively simple

complicated because the

about 100 kW.

- They are extremely

coolant temperature is

Efficiency of this technology is

flexible. and they can be

kept as low as possible to

ranging from 15% to 30%.

used as CHP (combined

maximize thermal

heat and power) in the

efficiency

winter and as coolers in summer Fuel Cells

Direct by hydrogen;

• Very high fuel efficiencies

• Few commercially

Fuel cell power systems are quiet,

natural gas, propane,

from hydrogen to electricity

available devices

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clean, highly efficient on-site

methanol, or other

• Potential to operate base

• Most research efforts are

electrical generators that use an

hydrogen-rich source

load with utility back-up

for automotive

electrochemical process—not

through reformer

• Possible residential

applications

combustion—to convert fuel into

application—a no-moving-

• Need for fuel reformer

electricity. In addition to providing

parts energy appliance

in almost all applications

power, they can supply a thermal

• Very high efficiencies

• Not a zero-emission

energy source for water and space

when combined with heat

technology—the effect of

heating, or absorption cooling. In

recovery

that may vary by state

demonstration projects, fuel cells

• Green technology—water

have been shown to reduce facility

and heat are only emissions

energy service costs by 20% to 40%

from hydrogen fuel, low

over conventional energy service.

emissions from other fuels

High temp: Efficiency is 45% to 55% Low temp: Efficiency is 30% to 40% • No variable costs for fuel

• Big foot print (600

Photovoltaic (PV) cells, or solar

• No moving parts—

ft²/kW)

cells, convert sunlight directly into

inexpensive maintenance

• High installed costs

electricity. PV cells are assembled

and long life

• Not suited for base load

into flat plate systems that can be

• No emissions, no noise

• Not suited for back-up

mounted on rooftops or other sunny

• Can be used for peak

except when accompanied

areas. They generate electricity with

shaving

by storage

no moving parts, operate quietly with

• Highly reliable, mature

• Variable energy output

no emissions, and require little

technology

Photovoltaic

None

maintenance. • No variable costs for fuel

• Need to meet siting

Wind turbines use the wind to

• In utility implementation,

requirements

produce electrical power. A turbine

zero emissions may allow

• Generation is

with fan blades is placed at the top of

green power price premium

intermittent with wind,

a tall tower. The tower is tall in order

• Mature technology

and energy output can

to harness the wind at a greater

• Multiple manufacturers

vary with wind speed

Large Wind Turbines

None

velocity, free of turbulence caused by

squared or cubed over

interference from obstacles such as

operation range. Not

trees, hills, and buildings. As the

appropriate as backup or

turbine rotates in the wind, a

off-grid applications

generator produces electrical power.

• Needs utility source for

A single wind turbine can range in

energy purchases and

size from a few kW for residential

sales

applications to more than 5 MW.

• Can require footprint up to 100ft²/kW

Table-1: Different Types of DG Technologies, Their Fuel Choices, Benefits and Drawbacks [26, 27] Different DG technologies are implemented to fulfil the requirements of a wide range of applications and these applications and technologies differ according to the load requirements (thermal needs, stand-alone or gridconnected electrical power, requirements of power quantity and environmental issues in the site, etc). Some of these applications are:

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-

Grid connection to sell the electrical energy,

-

Stand by sources to supply power for sensitive loads during grid outages,

-

Peak-load shaving,

-

Rural and remote applications,

-

Used local fuel resources,

-

Combined heat and power (CHP) with injection of power in to the network when the DG capacity is higher than its local load, and

-

Utility-owned DGs, to provide part of the main required power and support the grid by enhancing the system voltage profile, reducing the power losses, and improving the system power quality as well as reliability.

V. BENEFITS OF DG Countries like in India, many people are living in remote areas and they don‘t have access of electricity. Other side power deficiencies and Transmission & Distribution loss of power about 32% is in India [16]. Utilization of DG will lead to overcome of these issues. It provides more flexible and reliable power sources to consumers. It improves voltage instability connected with the power grid. There is more security provided by DG to the consumers due to setup of near to demand sites. We are considering economical, operational and environmental benefits of DG:

Fig.-2: Benefits of DG 5.1. Economical DGs can generates required demand of electricity by increasing installation of units at certain locations near to load sites, so they can reduce or avoid the need for building new transmission & distribution lines and upgrade the existing power systems [24, 26, 27]. Investment point of view, it is easier to find sites for DGs as compared to a large central power plant and such units can be online in much less time. Unnecessary capital expenditure avoided and capital exposure and risk are reduced by matching capacity increase with local demand growth. DGs can be assembled easily anywhere as modules for power generation which have many advantages as [28]:  In a very short period they can be installed at any location. Each modular can‘t be affected by other modular operation failure and operated immediately and separately after its installation independent of other modules arrival.  The total capacity can be increased or decreased by adding or removing more modules, respectively.

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Due to deregulation of electricity in many countries DGs will be of great importance in generating power locally especially if the location margin pricing (LMP) is applied for independent transmission operators (ISO‘s) and regional transmission organizations (RTO‘s). Location margin pricing (LMP) can give an indication of where DGs should be installed. Also by supplying power to the grid, DGs can reduce the wholesale price of power, which leads to reduction of the demand required [31]. DG can stimulate competition in supply; adjusting price via market forces. In a free market environment, DG operator can buy or sell power to the electricity grid, purchasing power at off-peak prices and exporting only at peak demand. DGs are decentralised power systems, so this has advantage to place at anywhere as per the demand. Flexibility of location for DG has a great effect on energy prices [29]. For the exact required customer load demand, DGs are well sized to be installed in small increments. However, renewable DGs technologies such as solar, wind, and hydro units require certain geographical and climatic conditions. As the demand for more and better quality electric power increases, DG can provide alternatives for costeffective, reliable, premium power for domestic use and for industrial use. When a power outage occurs at home or in the neighbourhood, restoring power in a short time, DG can provide customers with continuity and reliability of supply. By generating more power, CHP DGs can use their waste heat for improving their efficiency or heating and cooling, which is not applicable in the situation of centralized power generation alone [29]. For remote or stand-alone CHP DGs can be more economical [30]. DGs increase the system equipments and transformers lifetimes and provide fuel savings. According to different DGs technologies, the types of fuels and energy resources used are diversified. Therefore, there is no need for certain type of fuels or energy resources more than others [32]. Installation of DGs can reduce the construction schedules of developing plants. Hence, the system can track and follow the market‘s fluctuations and/or the peak-load demand growth [32]. All these technologies offer new market opportunities and enhanced industrial competitiveness.

5.2. Operational DGs can reduce the distribution network power losses [30, 32, 36, and 38], distribution loads requirements by supplying some of the distribution load demand, reduce power flow inside the transmission network to fit certain constraints and improve its voltage profile [36]. DGs have a positive impact on the distribution system voltage profile [30, 32, 38] and power quality problems [30, 31]. This technology can help in ―peak load shaving‖ and load management programs [34]. It can be used as on-site standby to supply electricity in case of emergency and system outages [36]. DGs maintain system stability, supply the spinning reserve required and they provide transmission capacity release [31]. It can be installed on medium and/or low voltage distribution network due to capacities vary from micro to large size which gives flexibility for sizing and site locating of DGs into the distribution network [37]. As there are many generation spots not only one centralized large generation so they can help in system continuity and reliability. When we are combined with DGs, there will be new customer classifications between high need for reliability with high service cost and others with less service cost and relatively lower reliability, especially in the case of end-user customers with low reliability [34]. From the mathematical point of view benefits of DG can be derived by figure-3 [19], which shows that the connection of a distributed generator to the power system, where R and X are the resistance and reactance of short-circuit, respectively, and Pg and Qg are the active and reactive power generated. According to Thevenin equivalent of the power system E is the voltage of the ideal source. At the same point of common coupling (PCC), there is a load characterised by its demand curve (Pload + jQload).

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Fig.-3: Connection of DG and load at the point of common coupling The variation of the voltage can be expressed as: ΔV = E – V = (R + jX)I = (R + jX)

=

+j

Where P and Q are the total active and reactive power absorbed from the power system (load + generation), respectively. The variation of the voltage at the PCC of the wind farm to the grid can be calculated by solving the following equation: V4 + [(RP + XQ) – E2]V2 + [(XP – RQ)2 + (XP + RQ)2] = 0 From the above expressions, the voltage at the point of common coupling is the result of the combination of several parameters and variables such as the active and reactive powers, and the characteristics of the network. Positive values of K and L imply injected powers. The management of Q permits adjustment of voltage at the PCC to the required level.

5.3. Environmental Development of highly efficient power generation (CHP production) and environmental friendly (renewable energy sources (RES)) has attracted significant attention around the world. With regard to, environment and society, renewable DGs eliminate or reduce the output process emission [39]. This is due to the increased awareness of the detrimental effects of the emissions from hydrocarbon based power stations on the environment, which has led to the commitment of many countries to comply with the Kyoto protocol [40] and reduce their green house gas (GHG) emissions. Power generation systems that use renewable resources like solar, wind, geothermal energy and organic matter have some advantages over traditional fossil –fuelled generation systems. For example, most renewable power technologies do not produces green house gases and emits far less pollution compared to burning oil, coal, or natural gas to generate electricity. It is widely recognised then the green house gas intensity in hydro-electrical systems is about 15g CO2 / KWh on average, 20g CO2 / KWh in the case of wind turbines and 100g CO2 / KWh for photovoltaic. Where as in classical thermal systems burning natural gas it is around 577g CO 2 / KWh (combined cycle) or 750g CO2 / KWh (open cycle) and in burning coal the values are greater than 860g CO2 / KWh [28, 29]. The environmental load is also reduced due to the avoidance of additional energy required to compensate transmission losses. Studies report that reduction of losses by 1% in the UK system reduces emissions by 2 million tonnes of CO2 per year [41]. Moreover, in the UK, reduction by 1 GWh from hydrocarbon can reduce emissions up to 400,000 tonnes per year. In selected Portuguese networks of various types, ranging from rural LV networks to HV ones, 20% penetration of DG reduces CO2 emissions by 2.07–4.85% [42]. It is demonstrated that on European scale, 65 million tonnes of CO2 per annum can be saved by 50 million installations of domestic CHP units. A significant impact of increased efficiency in the domestic utilisation of gas and electricity on the reduction of CO2 emissions is claimed in Pudjianto [43]. Next to the potential

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environmental benefits of DG, their economic evaluation is critically influenced by the developing CO2 emissions trading markets [44], which also affect production costs of electricity generated by thermal (hydrocarbon) units [41].

VI. CHALLENGES OF DG Today‘s power sectors are facing multiple challenges for example fuel shortage, environmental issues, power losses and government regulations. Like that, DGs are also having their own challenges. These challenges reduce overall performance of DG. Overcoming of these challenges will lead to optimal utilisation of DG. We considered four challenges of DG - commercial, technical, environmental, and regulatory. Inside this a technical challenge has three parts which are power quality, voltage rise effect and protection.

Fig.4: Challenges of DG 6.1. Commercial At present, distribution companies which businesses of wires have no incentives to connect DG and offer active management services. New commercial arrangements need to be developed to support the development of active distribution networks and extract corresponding benefits associated with connecting increased amount of DG. In General, possible three approaches can be [45]: o

To establish a market mechanism outside government regulations for the development of active networks that would create a commercial environment. Distribution companies charge for providing active management services to the generators. Clearly, this could be used as a basis for bilateral negotiations between the local company and the generator whenever the net benefit from active management exists.

o

To recover, cost of implementation of active management through the price controls mechanism (increasing the amount of recoverable capital and operating expenditure associated with active management). Recovery of cost could be achieved through increased charges for the use of the networks (distributed generators benefiting from either active management and/or demand customers).

o

Establishing an incentive scheme that would reward companies for connecting DG, which one is recently developed in the UK [46]. With a suitable design of the scheme, we can achieve development of active distribution networks for such incentive scheme. These types of scheme could be funded from increased charges imposed on generators and/or demand customers.

6.2. Technical There are some technical challenges of DG, among that power quality; voltage rise effect and protection are major challenges of DG. Further explanations of these issues are:

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6.2.1. Power Quality Power quality is an increasingly important issue especially in developing countries and generation of power is generally subject to the same regulations as loads. There are two aspects of power quality which are usually considered to be important [46]: (1) harmonic distortion of the network voltage and (2) transient voltage variations. DG plant can either increase or decrease the quality of the voltage received by other users of the distribution network which depends on the particular circumstances. 6.2.2. Voltage Rise Effect The voltage rise effect is a key factor that limits the amount of additional DG capacity that can be connected to rural distribution networks. Connection or disconnection of DG in distribution network causes voltage rise effect. It produces instability of power supply and power variations. We can control this by using optimal power flow under voltage step constraints [47, 48]. 6.2.3. Protection There are different aspects of DG protection which can be identified: protection of the faulted distribution network from fault currents supplied by the DG; protection of the generation equipment from internal faults; anti-islanding or loss-of-mains protection (due to penetration of DG increases, islanded operation of DG will be possible in future) and impact of DG on existing distribution system protection. For the connection of DG to the distribution networks, these aspects are important and should be carefully addressed [46].

6.3. Environmental After so many years of discussions and negotiations about sustainable development, the world‘s climate and its biodiversity are still deteriorating [18]. Environmental issues are prime concern for any countries due to increasing global warming and its negative impact over human being. Due to global warming our weather has changed and it becoming disaster for human life. From the fuel utilisation point of view, smaller distributed generation plants generally are less efficient than larger central plants of the same type. Only when operating in a CHP mode, they may conserve primary energy compared to the separate generation of electricity and heat in best available technology (BAT)-electric-power plants and high-efficiency boilers. It is not easy to locate the environmental burden per unit of output (electricity or heat) in that the allocation of the emissions to the electricity or heat side is not straightforward. Based on direct or avoided emissions this allocation may be done energetically or exergetically. Although there are good thermodynamic reasons for argue over the most justified allocation which is based on the exergetic philosophy of avoided emissions, it is recommended to avoid the allocation and to compare CHP with separate generation. The primary power saving of CHP compared to separate generation is PPS = ( Where,

)F and

(1)

are the electric and thermal efficiencies of the CHP, respectively,

and

are electric and

thermal efficiencies of the electric power plant and the boiler in the case of separate generation and F is the fuel input power in the CHP. With compression ignition (CI) the emission coefficient of the primary driver (gas turbine, engine, etc.) of the CHP per unit primary input i.e, CI =

(2)

Avoided emission of the CHP per unit of primary fuel input in the CHP compared to separate generation is

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International Journal of Science, Technology & Management Volume No 04, Special Issue No. 01, March 2015 Avoided emissions = (

)CI


(3)

This represents that the increased use of distributed generation is not always beneficial for the environment. For some cases or applications DG would be beneficial for environment, but in general it would not be. The outcome will crucially depend on the market share of the different DG technologies and on the mix of central generation that is replaced [20]. As far as renewable DG units are concerned, only indirect emissions have to be taken into account. Voorspools et al. [49] considered about indirect emission in their work.

6.4. Regulatory On the treatment of DG, it is very unlikely that this type of generation is going to thrive in the absence of a clear policy and associated regulatory instruments. For this, the reasons are partly historical and related to the way distribution networks have been developed and operated as passive networks. In order to foster the required changes that support the integration of DG into distribution networks, there is a clear need to develop and articulate appropriate policies [46].

VII. CONCLUSIONS The setback associated with central power generation has necessitated the development of DG. The area has attracted the attention of power generation and distribution sector. We discussed over the topic of DG in our work, and focused on how DG can be a better replacement of central power generation system. We have discussed about multidimensional benefits of DG along with their setbacks for better analysis. We have gone through different types of DG technology with their benefits and drawbacks. In this work, we focused over renewable energy sources and their increasing demand in DG. Further we elaborate advantage of renewable distributed generation to reduce carbon emission. Along with penetration of renewable energy sources in DG, we discussed over transmission and distribution losses minimization and flexibility of DG. Adaptation of DG in power sector is still in its infancy state and is addressed along with challenges of DG in this paper. Further developments and more research work would be realized over the next few years to overcome these challenges. Having DG system that addresses the above research issues would accelerate the economical and environmental impact of DG in development of human life. Further research is required for finding optimal allocation and size of DG under load demand uncertainty and stochastically distributed solar and wind energy. Also there is need of research over DG to make this feasible for rural areas in developing countries.

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an overview of distributed generation in power sector - IJSTM

an overview of distributed generation in power sector - IJSTM

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